Ethylene-vinyl alcohol copolymer and preparation process thereof

Abstract

The invention discloses an ethylene-vinyl alcohol copolymer and a preparation process thereof, and relates to the technical field of EVOH. According to the preparation process of the ethylene-vinyl alcohol copolymer, through gradient control of EVA polymerization and alcoholysis process conditions, on one hand, uniform control of heat release in a polymerization stage and an alcoholysis stage can be realized, heat in each stage is fully utilized, and the conversion rate and alcoholysis efficiency in the polymerization process are improved; on the other hand, effective regulation and control of EVOH composition, molecular weight distribution, molecular chain sequence structure and stereoregularity can be realized; finally, side reactions in the polymerization stage and the alcoholysis stage can be reduced, and generation of gel and impurities is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of EVOH, in particular to an ethylene-vinyl alcohol copolymer and a preparation process thereof. Background Art

[0002] Ethylene-vinyl alcohol copolymer (EVOH) combines the properties of polyethylene and polyvinyl alcohol. It is a widely used resin material with high barrier properties and solvent resistance. Therefore, it is widely used in food, medical and cosmetic packaging, as well as automotive fuel tanks, industrial pipelines and other fields. The ethylene and vinyl alcohol segments in the EVOH polymer chain are statistically distributed. The ethylene segments give it flexibility, making it more processable than polyvinyl alcohol. The vinyl alcohol segments, through strong intramolecular and intermolecular hydrogen bonding, reduce the free volume within the polymer network, making it difficult for small molecules such as gases and solvents to diffuse through, giving it excellent gas barrier properties and solvent resistance. The number and distribution of these two units directly determine the properties of EVOH. Therefore, controlling the number and distribution of the two repeating units in EVOH is crucial for regulating EVOH's performance.

[0003] The core control point of the EVOH production process is the regulatory relationship between molecular structure, sequence structure, degree of branching, and crystallization. Currently, conventional EVOH production processes primarily utilize one-shot continuous or intermittent batch polymerization methods, which are unable to effectively control the polymerization gradient. Therefore, it is crucial to control the reactivity ratio of ethylene and vinyl acetate by matching the temperature and pressure during the polymerization stage to achieve transition and synergy between the copolymerization forms, control the product composition and sequence structure, and regulate the alcoholysis rate and depth by controlling the alcoholysis stage to improve product properties and sodium salt residue to avoid affecting the performance and appearance of EVOH. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: to overcome the shortcomings of the existing technology, provide an ethylene-vinyl alcohol copolymer and a preparation process thereof, prepare EVOH by respectively carrying out polymerization of EVA and alcoholysis of EVA in a tubular reactor, and combine the staged control of temperature, pressure and alcoholysis catalyst concentration and segmented feeding, while efficiently removing the reaction heat, achieving effective regulation of the molecular weight distribution, molecular chain sequence structure and stereoregularity, and improving the reaction conversion rate, alcoholysis efficiency and degree.

[0005] The technical solution of the present invention is: In one aspect, the present invention provides a process for preparing an ethylene-vinyl alcohol copolymer, comprising the following steps: S1 polymerization stage: Ethylene, alcohol solvent, vinyl acetate and initiator are introduced into a tubular reactor to carry out free radical polymerization at 50-100°C and 3-6 MPaG; S2 residual monomer removal stage: adding a polymerization inhibitor to terminate the reaction, removing unreacted ethylene and vinyl acetate, and obtaining a solution containing ethylene-vinyl acetate copolymer; S3 alcoholysis stage: adding a catalyst and carrying out alcoholysis reaction at 60-100°C to obtain a solution containing ethylene-vinyl alcohol copolymer; S4 post-treatment: acid-washing, water-washing and drying the solution containing the ethylene-vinyl alcohol copolymer to obtain the ethylene-vinyl alcohol copolymer; In step S1, the free radical polymerization reaction is carried out by a temperature gradient polymerization method or a pressure gradient polymerization method, wherein the temperature gradient polymerization method is to first carry out polymerization in the first polymerization section of the tubular reactor and then carry out polymerization in the second polymerization section of the tubular reactor, and the reaction temperature of the second polymerization section is higher than the reaction temperature of the first polymerization section; the pressure gradient polymerization method is to first carry out polymerization in the first polymerization section of the tubular reactor and then carry out polymerization in the second polymerization section of the tubular reactor, and the pressure of the second polymerization section is higher than the pressure of the first polymerization section; Meanwhile, in step S1, when temperature gradient polymerization is adopted, the initiator added in the first polymerization stage is azobisisobutyronitrile, azobiscyanovaleric acid or dilauroyl peroxide, and the initiator added in the second polymerization stage is azobiscyclohexylcarbonitrile or tert-butyl peroxy-2-ethylhexanoate; In step S3, at least one of a temperature gradient alcoholysis method and a catalyst concentration gradient alcoholysis method is adopted during the alcoholysis reaction, wherein the temperature gradient alcoholysis method is to first carry out alcoholysis in the alcoholysis section 1 of the tubular reactor and then carry out alcoholysis in the alcoholysis section 2 of the tubular reactor, and the reaction temperature of the alcoholysis section 2 is higher than the reaction temperature of the alcoholysis section 1; the catalyst concentration gradient alcoholysis method is to first carry out alcoholysis in the alcoholysis section 1 of the tubular reactor and then carry out alcoholysis in the alcoholysis section 2 of the tubular reactor, and the mass ratio of the catalyst added in the alcoholysis section 2 to the catalyst added in the alcoholysis section 1 is (2-3):1; and the molar ratio of the catalyst to the vinyl acetate unit in the ethylene-vinyl acetate copolymer in the alcoholysis section 1 and the alcoholysis section 2 is (0.01-0.03):1.

[0006] Preferably, in step S1, the alcohol solvent is C1-C4 alcohol, specifically methanol or tert-butanol, and the added amount is 5-20 wt.% of the vinyl acetate.

[0007] Preferably, in step S1, the amount of the initiator added is 0.01-0.04% of the total mass of vinyl acetate and ethylene.

[0008] Preferably, in step S1, the free radical polymerization reaction time of the first polymerization stage and the second polymerization stage is 1-3 hours respectively.

[0009] Preferably, in step S2, the polymerization inhibitor is hydroquinone, 2,4-diphenyl-4-methyl-1-pentene, tert-dodecyl mercaptan or copper acetate, and the added amount is 0.005-0.05 wt.% of vinyl acetate.

[0010] Preferably, in step S3, the catalyst is an alkaline catalyst, specifically sodium hydroxide.

[0011] Preferably, in step S3, the reaction time of the alcoholysis section 1 and the alcoholysis section 2 is 1-3 h, respectively.

[0012] Preferably, in step S4, the acid used for pickling is acetic acid, boric acid or phosphoric acid, and the molar ratio of the acid to the catalyst in step S3 is (0.5-2):1.

[0013] Preferably, in step S4, the drying temperature is 60-120°C.

[0014] In another aspect, the present invention provides an ethylene-vinyl alcohol copolymer prepared by the above-mentioned process for preparing the ethylene-vinyl alcohol copolymer.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The preparation process of the ethylene-vinyl alcohol copolymer of the present invention can achieve uniform control of heat release in the polymerization stage and the alcoholysis stage through gradient control of EVA polymerization and alcoholysis process conditions, fully utilize the heat in each stage, and improve the conversion rate and alcoholysis efficiency of the polymerization process; on the other hand, it can achieve effective regulation of EVOH composition, molecular weight distribution, molecular chain sequence structure and stereoregularity; finally, it can reduce side reactions in the polymerization stage and the alcoholysis stage, and reduce the generation of gel and impurities. DETAILED DESCRIPTION

[0016] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0017] Example 1 The preparation process of the ethylene-vinyl alcohol copolymer of this embodiment comprises the following steps: S1 polymerization stage: the entire tubular reactor was replaced with nitrogen three times, and then replaced with ethylene twice, and ethylene was introduced to maintain the reaction pressure at 3.5 MPaG; initiators azobiscyanovaleric acid, methanol and vinyl acetate were injected into the polymerization section 1 of the tubular reactor, wherein the initiator amount was 0.02% of the total mass of vinyl acetate and ethylene, and the methanol amount was 5wt.% of vinyl acetate, and free radical polymerization was carried out at 50°C for 3 hours; then transferred to the polymerization section 2, the initiator azobiscyclohexylcarbonitrile was injected, the amount was 0.01% of the total mass of vinyl acetate and ethylene, and free radical polymerization was carried out at 100°C for 1 hour.

[0018] S2 residual monomer removal stage: hydroquinone is added at 100 ppm of vinyl acetate to terminate the reaction, and unreacted ethylene and vinyl acetate are removed to obtain a solution containing EVA.

[0019] S3 alcoholysis stage: transfer to the alcoholysis section 1 of the tubular reactor, inject the catalyst NaOH with a molar ratio of 0.02:1 to the vinyl acetate unit in EVA, and carry out alcoholysis reaction at 60°C for 2 hours; then transfer to the alcoholysis section 2, inject the catalyst NaOH with a molar ratio of 0.02:1 to the vinyl acetate unit in EVA, and carry out alcoholysis reaction at 90°C for 2 hours, and finally obtain a solution containing EVOH.

[0020] S4 post-treatment: Pour the solution containing EVOH into pure water dissolved with acetic acid for acid washing and neutralization, where the molar ratio of acetic acid to sodium hydroxide added in step S3 is 1:1, and then wash with pure water three times. After filtering, a precipitate is obtained; the precipitate is placed in a vacuum oven at 60°C and dried for 24 hours to obtain EVOH.

[0021] Example 2 The preparation process of the ethylene-vinyl alcohol copolymer of this embodiment comprises the following steps: S1 polymerization stage: the entire tubular reactor was replaced with nitrogen three times, and then replaced with ethylene twice. In the polymerization section 1 of the tubular reactor, ethylene was introduced to maintain the reaction pressure at 3 MPaG, and initiators azobisisobutyronitrile, tert-butanol and vinyl acetate were injected, wherein the amount of initiator was 0.01% of the total mass of vinyl acetate and ethylene, and the amount of tert-butanol was 20 wt.% of vinyl acetate, and free radical polymerization was carried out at 50°C for 3 hours; then the reactor was transferred to the polymerization section 2, ethylene was introduced to maintain the reaction pressure at 5 MPaG, and free radical polymerization was carried out at 50°C for 1 hour.

[0022] S2 residual monomer removal stage: add 200 ppm of copper acetate based on vinyl acetate to terminate the reaction, remove unreacted ethylene and vinyl acetate, and obtain a solution containing EVA.

[0023] S3 alcoholysis stage: transfer to the alcoholysis section 1 of the tubular reactor, inject the catalyst NaOH with a molar ratio of 0.02:1 to the vinyl acetate unit in EVA, and carry out alcoholysis reaction at 80°C for 2 hours; then transfer to the alcoholysis section 2, inject the catalyst NaOH with a molar ratio of 0.02:1 to the vinyl acetate unit in EVA, and carry out alcoholysis reaction at 100°C for 2 hours, and finally obtain a solution containing EVOH.

[0024] S4 post-treatment: Pour the solution containing EVOH into pure water dissolved with boric acid for pickling and neutralization, where the molar ratio of boric acid to sodium hydroxide added in step S3 is 2:1, and then wash with pure water three times. After filtering, a precipitate is obtained; the precipitate is placed in a vacuum oven at 120°C and dried for 6 hours to obtain EVOH.

[0025] Example 3 The preparation process of the ethylene-vinyl alcohol copolymer of this embodiment comprises the following steps: S1 polymerization stage: the entire tubular reactor was replaced with nitrogen three times, and then replaced with ethylene twice, and ethylene was introduced to maintain the reaction pressure at 3.5 MPaG; in the polymerization section 1 of the tubular reactor, the initiators dilauroyl peroxide, methanol and vinyl acetate were injected, wherein the initiator amount was 0.01% of the total mass of vinyl acetate and ethylene, and the methanol amount was 10wt.% of vinyl acetate, and a free radical polymerization reaction was carried out at 60°C for 2h; then transferred to the polymerization section 2, the initiator tert-butyl peroxide-2-ethylhexanoate was injected, the amount was 0.03% of the total mass of vinyl acetate and ethylene, and a free radical polymerization reaction was carried out at 90°C for 1h.

[0026] S2 residual monomer removal stage: 50 ppm of tert-dodecyl mercaptan based on vinyl acetate is added to terminate the reaction, remove unreacted ethylene and vinyl acetate, and obtain a solution containing EVA.

[0027] S3 alcoholysis stage: transfer to the alcoholysis section 1 of the tubular reactor, inject the catalyst NaOH with a molar ratio of 0.01:1 to the vinyl acetate unit in EVA, and carry out alcoholysis reaction at 90°C for 3 hours; then transfer to the alcoholysis section 2, inject the catalyst NaOH with a molar ratio of 0.03:1 to the vinyl acetate unit in EVA, and continue the alcoholysis reaction at 90°C for 1 hour, and finally obtain a solution containing EVOH.

[0028] S4 post-treatment: Pour the solution containing EVOH into pure water dissolved in phosphoric acid for acid washing and neutralization, where the molar ratio of phosphoric acid to sodium hydroxide added in step S3 is 0.5:1, and then wash with pure water three times. After filtering, a precipitate is obtained; the precipitate is placed in a vacuum oven at 80°C and dried for 16 hours to obtain EVOH.

[0029] Example 4 The preparation process of the ethylene-vinyl alcohol copolymer of this embodiment comprises the following steps: S1 polymerization stage: the entire tubular reactor was replaced with nitrogen three times, and then replaced with ethylene twice, and ethylene was introduced to maintain the reaction pressure at 6 MPaG; initiators dilauroyl peroxide, tert-butyl alcohol and vinyl acetate were injected into the polymerization section 1 of the tubular reactor, wherein the initiator amount was 0.01% of the total mass of vinyl acetate and ethylene, and the tert-butyl alcohol amount was 15wt.% of vinyl acetate, and free radical polymerization was carried out at 60°C for 2h; then transferred to the polymerization section 2, the initiator tert-butyl peroxy-2-ethylhexanoate was injected, the amount was 0.03% of the total mass of vinyl acetate and ethylene, and free radical polymerization was carried out at 90°C for 1h.

[0030] S2 residual monomer removal stage: 2,4-diphenyl-4-methyl-1-pentene is added at 500 ppm of vinyl acetate to terminate the reaction, remove unreacted ethylene and vinyl acetate, and obtain a solution containing EVA.

[0031] S3 alcoholysis stage: transfer to the alcoholysis section 1 of the tubular reactor, inject the catalyst NaOH with a molar ratio of 0.01:1 to the vinyl acetate unit in EVA, and carry out alcoholysis reaction at 60°C for 2 hours; then transfer to the alcoholysis section 2, inject the catalyst NaOH with a molar ratio of 0.02:1 to the vinyl acetate unit in EVA, and continue the alcoholysis reaction at 100°C for 2 hours to finally obtain a solution containing EVOH.

[0032] S4 post-treatment: pour the solution containing EVOH into pure water dissolved with acetic acid for acid washing and neutralization, where the molar ratio of acetic acid to sodium hydroxide added in step S3 is 1:1, and then wash with pure water three times. After filtering, a precipitate is obtained; the precipitate is placed in a vacuum oven at 100°C and dried for 10 hours to obtain EVOH.

[0033] Comparative Example 1 The difference from Example 1 is that, in step S1, in the polymerization stage, the entire tubular reactor was replaced with nitrogen three times, then with ethylene twice, and ethylene was introduced to maintain the reaction pressure at 3.5 MPaG; initiators azobiscyanovaleric acid, methanol, and vinyl acetate were injected into the polymerization section 1 of the tubular reactor, wherein the amount of initiator was 0.03% of the total mass of vinyl acetate and ethylene, and the amount of methanol was 5 wt.% of vinyl acetate, and a free radical polymerization reaction was carried out at 50°C for 4 hours.

[0034] Comparative Example 2 The difference from Example 1 is that, in step S3, the alcoholysis stage is transferred to the alcoholysis section 1 of the tubular reactor, a catalyst NaOH having a molar ratio of 0.04:1 to the vinyl acetate unit in EVA is injected, and the alcoholysis reaction is carried out at 60° C. for 4 hours to finally obtain a solution containing EVOH.

[0035] Comparative Example 3 The difference from Example 1 is that, in step S1, during the polymerization stage, the entire tubular reactor was purged with nitrogen three times, then with ethylene twice, with ethylene introduced to maintain the reaction pressure at 3.5 MPaG; into the polymerization section 1 of the tubular reactor, initiators azobiscyanovaleric acid, methanol, and vinyl acetate were injected, wherein the initiator amount was 0.03% of the total mass of vinyl acetate and ethylene, and the methanol amount was 5 wt.% of the vinyl acetate, and a free radical polymerization reaction was carried out at 50°C for 4 hours. Simultaneously, in step S3, during the alcoholysis stage, the catalyst NaOH was injected into the alcoholysis section 1 of the tubular reactor at a molar ratio of 0.04:1 to the vinyl acetate units in the EVA, and an alcoholysis reaction was carried out at 60°C for 4 hours, ultimately yielding a solution containing EVOH.

[0036] Comparative Example 4 The difference from Example 2 is that in step S1, during the polymerization stage, the entire tubular reactor was replaced with nitrogen three times and then with ethylene twice. In the polymerization section 1 of the tubular reactor, ethylene was introduced to maintain the reaction pressure at 3 MPaG, and initiators azobisisobutyronitrile, tert-butanol, and vinyl acetate were injected, wherein the amount of the initiator was 0.01% of the total mass of vinyl acetate and ethylene, and the amount of tert-butanol was 20 wt.% of vinyl acetate. Free radical polymerization was carried out at 50°C for 4 hours.

[0037] Comparative Example 5 The difference from Example 2 is that, in step S1, the polymerization stage: the entire tubular reactor is replaced with nitrogen three times, then replaced with ethylene twice, and in the polymerization section 1 of the tubular reactor, ethylene is introduced to maintain the reaction pressure at 3 MPaG, and initiators azobisisobutyronitrile, tert-butyl alcohol, and vinyl acetate are injected, wherein the initiator amount is 0.01% of the total mass of vinyl acetate and ethylene, and the tert-butyl alcohol amount is 20 wt.% of vinyl acetate, and a free radical polymerization reaction is carried out at 50°C for 4 hours. At the same time, in step S3, the alcoholysis stage: the tubular reactor is transferred to the alcoholysis section 1, and the catalyst NaOH is injected at a molar ratio of 0.04:1 to the vinyl acetate unit in EVA. The alcoholysis reaction is carried out at 80°C for 4 hours, and finally a solution containing EVOH is obtained.

[0038] Comparative Example 6 The difference from Example 3 is that, in step S3, the alcoholysis stage: the mixture is transferred to the alcoholysis section 1 of the tubular reactor, and the catalyst NaOH is injected at a molar ratio of 0.04:1 to the vinyl acetate unit in EVA, and the alcoholysis reaction is carried out at 90°C for 4 hours to finally obtain a solution containing EVOH.

[0039] The process conditions and EVOH test results of Examples 1-4 and Comparative Examples 1-6 are shown in Table 1: Table 1 Process conditions and EVOH test results of Examples 1-4 and Comparative Examples 1-6

[0040] As shown in Table 1, Examples 1-4 of the present invention employ gradient polymerization and gradient alcoholysis techniques. This allows for molecular structure control during the polymerization stage, improving polymerization conversion, reducing molecular weight distribution, and obtaining EVOH products with suitable stereoregularity (meso stereo fraction). Furthermore, it controls the alcoholysis reaction rate, reduces side reactions, and improves the alcoholysis degree of the final EVOH product. However, Comparative Example 1 lacks a high-temperature polymerization stage, resulting in a low polymerization conversion. Comparative Example 2 lacks a high-temperature alcoholysis stage, resulting in a low alcoholysis degree. Comparative Example 3 lacks a high-temperature polymerization stage, and Comparative Examples 4-5 lack a high-pressure polymerization stage, resulting in low conversion and inappropriate stereoregularity. Furthermore, Comparative Examples 3 and 5 also lack a high-temperature alcoholysis stage, resulting in a low alcoholysis degree. While Comparative Example 6 achieves a high polymerization conversion, the high catalyst concentration in the alcoholysis stage results in an excessively vigorous alcoholysis process, which in turn reduces product performance to some extent.

Claims

1. A process for preparing an ethylene-vinyl alcohol copolymer, characterized in that: The following steps are involved: S1 polymerization stage: Ethylene, alcohol solvent, vinyl acetate and initiator are introduced into a tubular reactor to carry out free radical polymerization at 50-100°C and 3-6 MPaG; S2 residual monomer removal stage: adding a polymerization inhibitor to terminate the reaction, removing unreacted ethylene and vinyl acetate, and obtaining a solution containing ethylene-vinyl acetate copolymer; S3 alcoholysis stage: adding a catalyst and carrying out alcoholysis reaction at 60-100°C to obtain a solution containing ethylene-vinyl alcohol copolymer; S4 post-treatment: acid-washing, water-washing and drying the solution containing the ethylene-vinyl alcohol copolymer to obtain the ethylene-vinyl alcohol copolymer; In step S1, the free radical polymerization reaction is carried out by a temperature gradient polymerization method or a pressure gradient polymerization method, wherein the temperature gradient polymerization method is to first carry out polymerization in the first polymerization section of the tubular reactor and then carry out polymerization in the second polymerization section of the tubular reactor, and the reaction temperature of the second polymerization section is higher than the reaction temperature of the first polymerization section; the pressure gradient polymerization method is to first carry out polymerization in the first polymerization section of the tubular reactor and then carry out polymerization in the second polymerization section of the tubular reactor, and the pressure of the second polymerization section is higher than the pressure of the first polymerization section; Meanwhile, in step S1, when temperature gradient polymerization is adopted, the initiator added in the first polymerization stage is azobisisobutyronitrile, azobiscyanovaleric acid or dilauroyl peroxide, and the initiator added in the second polymerization stage is azobiscyclohexylcarbonitrile or tert-butyl peroxy-2-ethylhexanoate; In step S3, at least one of a temperature gradient alcoholysis method and a catalyst concentration gradient alcoholysis method is adopted during the alcoholysis reaction, wherein the temperature gradient alcoholysis method is to first carry out alcoholysis in the alcoholysis section 1 of the tubular reactor and then carry out alcoholysis in the alcoholysis section 2 of the tubular reactor, and the reaction temperature of the alcoholysis section 2 is higher than the reaction temperature of the alcoholysis section 1; the catalyst concentration gradient alcoholysis method is to first carry out alcoholysis in the alcoholysis section 1 of the tubular reactor and then carry out alcoholysis in the alcoholysis section 2 of the tubular reactor, and the mass ratio of the catalyst added in the alcoholysis section 2 to the catalyst added in the alcoholysis section 1 is (2-3):1; and the molar ratio of the catalyst to the vinyl acetate unit in the ethylene-vinyl acetate copolymer in the alcoholysis section 1 and the alcoholysis section 2 is (0.01-0.03):

1.

2. The process for preparing the ethylene-vinyl alcohol copolymer according to claim 1, wherein: In step S1, the alcohol solvent is methanol or tert-butanol, and the added amount is 5-20 wt.% of vinyl acetate.

3. The process for preparing the ethylene-vinyl alcohol copolymer according to claim 1, wherein: In step S1, the amount of initiator added is 0.01-0.04% of the total mass of vinyl acetate and ethylene.

4. The process for preparing the ethylene-vinyl alcohol copolymer according to claim 1, wherein: In step S1, the free radical polymerization reaction time of the polymerization section 1 and the polymerization section 2 is 1-3 hours respectively.

5. The process for preparing the ethylene-vinyl alcohol copolymer according to claim 1, wherein: In step S2, the polymerization inhibitor is hydroquinone, 2,4-diphenyl-4-methyl-1-pentene, tert-dodecyl mercaptan or copper acetate, and the added amount is 0.005-0.05 wt.% of vinyl acetate.

6. The process for preparing the ethylene-vinyl alcohol copolymer according to claim 1, wherein: In step S3, the catalyst is sodium hydroxide.

7. The process for preparing the ethylene-vinyl alcohol copolymer according to claim 1, wherein: In step S3, the reaction time of the alcoholysis section 1 and the alcoholysis section 2 is 1-3 hours respectively.

8. The process for preparing ethylene-vinyl alcohol copolymer according to claim 1, wherein: In step S4, the acid used for pickling is acetic acid, boric acid or phosphoric acid, and the molar ratio of the acid to the catalyst in step S3 is (0.5-2):

1.

9. The process for preparing the ethylene-vinyl alcohol copolymer according to claim 1, wherein: In step S4, the drying temperature is 60-120°C.

10. Ethylene-vinyl alcohol copolymer, characterized in that The ethylene-vinyl alcohol copolymer is prepared by the preparation process of any one of claims 1 to 9.

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